Friday, February 03, 2017

The war raging in your backyard

The battle is joined.

There's a lot more going on in your backyard than you suspect. To combat opponents that can bite, pinch, fly, crawl, and run, plants have developed an impressive suite of chemical weapons. Kate Horowitz writes:

Some of these weapons are poison; others simply make the plants taste awful. And then there are the wasp calls. When under attack, some plants emit volatile gases that act almost like dog whistles, silently summoning gangs of parasitic wasps to take care of the offending insect.

Even without the benefit of external sensory organs, plants can tell when they’re being assaulted. Previous studies have found that some plants can sense their attackers’ odors in the air. Others ‘listen’ for the chemical distress calls emitted by nearby plants. Still others pick up on chemicals in a slobbering bug’s saliva.

So lots of plants can tell when they’re being eaten, but can they tell who’s doing the eating? To find out, researchers paired field mustard (Brassica rapa) plants with 12 different herbivore species, including caterpillars, aphids, and a slug. Some species were gnawers and chewers, while others fed via sucking. Some were local and some were unfamiliar. The researchers covered each plant/pest pair with a plastic bag to collect any gases the plants emitted, then tested the gas.

The plants were having none of it. They fought back admirably against all 12 attackers, producing different compounds for each species in order to summon the right species of wasp. The gases all contained the same chemicals; the plants simply adjusted the ratio of chemicals to customize each cocktail. They even concocted successful blends to dispose of species they’d never met before.